1. Field of the Invention
The field of the present invention is gas detection apparatus, and, more particularly, laser apparatus for methane gas detection.
2. Description of the Prior Art
Gas detection systems utilizing lasers tuned to one of the natural absorption lines of the gas molecular species to be detected have been the subject of discussion in the literature. Exemplary of the prior art is the gas monitoring system described in U.S. Pat. No. 3,788,742 ("Garbuny"). This system includes a laser tuned to a wavelength coincident with a natural absorption line of the gas molecular species to be detected. The apparatus is not directed specifically to methane gas, but purports to be tunable and applicable to a range of gas molecular species. A detector is phase locked to the laser assembly by a lock-in amplifier.
The paper "Methane Gas Detection Using a Laser," by H.J. Gerritsen, published in SME Transactions, Dec. 1966, describes a gas detection system utilizing a helium neon laser.
U.S. Pat. Nos. 3,793,525 and 3,832,548 disclose synchronous detection of light beams which have passed through gas samples being analyzed by receivers remote from the transmitter.
The paper "Characteristics of a Laser System for Atmospheric Absorption and Air Pollution Experiments" by Z. Kucerovsky, E. Braunen, K. C. Paulekat and D. G. Rumbold, published in the Journal of Applied Meteorology in Dec. 1973, Volume 12, pp. 1387-1392, discusses a double-beam laser transmitter and receiver system for measuring the concentration of methane in the atmosphere and detection of methane point leaks.
The paper "Pollutant Detection By Absorption Using Mie Scattering and Topographical Targets as Retroreflectors," by Robert L. Byer and Max Garbuny, published in Applied Optics, Volume 12, No. 7, pp. 1496-1505, July, 1973, discusses pollution detection using backscattered laser radiation.
The paper "Remote Detection of CO by Parametric Tunable Laser", by T. Henningsen and M. Garbuny, published in Applied Physics Letters, Vol. 24, No. 5, Mar. 1, 1974, discusses a transmitter-receiver system for remote detection of carbon monoxide by using topographical features or atmospheric aerosol as the backscattering means.
Insofar as is known, however, the prior art research and development activities have not resulted in any practical, easily portable single-ended methane leak detectors employing low power lasers.